Wireless Circuit Breaker Interrogator (WCBI)Final Report

Team number: May02-11

Date submitted: 5/8/02

Client: Square D Company

Client contact: Greg Wiese

Faculty advisors: Glenn HilleslandJames Triska

Technical advisors: Mani MinaSteve Russell

Team members: Fahad AzeemMatt HenslerNeil PetersonGreg Stamp

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Table of ContentsList of Tables.......................................................................................................................iiList of Figures......................................................................................................................iiExecutive Summary.............................................................................................................1Acknowledgement...............................................................................................................1Definition of Terms.............................................................................................................1Introduction..........................................................................................................................2

General Background........................................................................................................2Technical Problem...........................................................................................................2Operating Environment...................................................................................................3Intended User(s) and Use(s)............................................................................................3Assumptions....................................................................................................................3Limitations.......................................................................................................................3

Design Requirements...........................................................................................................4Design Objectives............................................................................................................4Functional Requirements.................................................................................................4Design Constraints...........................................................................................................4Measurable Milestones....................................................................................................5

End-Product Description.....................................................................................................5Approach and Design..........................................................................................................5

Technical Approaches.....................................................................................................5Technical Design.............................................................................................................6Testing Description..........................................................................................................9Risks and Risk Management.........................................................................................10Recommendations for Follow-On Work.......................................................................10

Financial Budget................................................................................................................10Personnel Effort Budget....................................................................................................11Project Schedule................................................................................................................11Evaluation of Project Success............................................................................................13Commercialization.............................................................................................................13Recommendations for Additional Work............................................................................14Lessons Learned................................................................................................................14Project Team Information..................................................................................................15

Team Members..............................................................................................................15Faculty advisors.............................................................................................................15Technical Advisors........................................................................................................16Client..............................................................................................................................16

Summary............................................................................................................................16References..........................................................................................................................17

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List of TablesTable 1 - Wire/Connection relationship..............................................................................9Table 2 - Financial budget.................................................................................................11Table 3 - Overall personnel effort budget..........................................................................11

List of FiguresFigure 1 - Existing system...................................................................................................6Figure 2 - First proposed solution........................................................................................6Figure 3 – Second proposed solution...................................................................................7Figure 4 - Final Solution......................................................................................................8Figure 5 - MicroHopper connector schematic.....................................................................9Figure 6 - First semester schedule (original and revised)..................................................12Figure 7 - Second semester schedule (original and revised).............................................12

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Executive SummaryElectronic control units on industrial circuit breakers are used to store information about the breaker including its settings and trip history. Certain monitoring equipment can be connected to these electronic controls in order to download information about the breaker to a personal computer. This method requires a direct connection between a laptop computer and the control unit. The purpose of this project was to develop a wireless connection, having the ability to efficiently interrogate the breaker control unit. This solution will be used by Square D to demonstrate to its marketing department the feasibility of a wireless interrogation system.

The wireless connection uses transceivers that use spread spectrum and operate in the 915 MHz ISM band. This was accomplished by purchasing World Wireless Communications 900 SS MicroHopper data radio with the appropriate serial communication interfaces. This device was implemented by making the appropriate modifications to the radio’s serial connections.

The final solution consisted of a transceiver attached to a laptop and two transceivers attached to separate BCMs. This system functioned properly and met all of the project requirements.

AcknowledgementSquare D has provided the trip units, breaker control modules, and software for the existing system. They also purchased the MicroHopper data radios. In addition, they have contributed technical assistance in demonstrating the existing interrogation system. In addition to technical advisor support, Dr. Robert Weber has offered some assistance with the technical design of the project.

Definition of TermsASK-amplitude shift keyingBCM-breaker control/communication moduleDSSS-direct sequencing spread spectrumEMI-electro magnetic interferenceFHSS-frequency hopping spread spectrumFSK-frequency shift keyingGUI-graphical user interfaceIC-integrated circuitISM-industrial scientific and medicalkbps-kilobits per second MODBUS-industry standard software protocol used for transmissions over serial linesOOK-on-off keyingPC-personal computer

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PC card-a type of computer interfaceRS 232-recommended standard 232: full duplex serial communicationRS 485-recommended standard 485: 4-wire, half-duplex serial communicationRTS-ready to sendRX#-receiver IC, channel #SAW- surface acoustic waveTU-trip unit: monitors and controls circuit breaker settingsTX#-transmitter IC, channel #USB-universal serial busWCBI-wireless circuit breaker interrogator

Introduction

General Background

Many industrial circuit breakers have trip units (TUs) that monitor the breaker settings such as voltage and current levels necessary to cause a trip event. The trip units also monitor the tripping history information such as voltage, current and time of a trip event. Communication with the TUs currently requires a direct connection between the BCMs (attached to the TUs) and a laptop. The user has software that displays the information on the laptop screen. The current system makes interrogation of circuit breakers cumbersome and requires disabling power to the breakers when BCMs are wired incorrectly. A wireless link has been developed that allows someone using a laptop computer to communicate with the trip units. The MicroHopper transceivers connect to the laptop and BCMs to create the wireless circuit breaker interrogator, or WCBI. The complete wireless system reduces time spent on wiring troubleshooting and will speed the process of circuit breaker interrogation.

Technical Problem

Wireless communication hardware was chosen in order to implement this wireless system. Different factors such as choosing licensed versus unlicensed frequency ranges, transmission range, interference issues, availability of hardware, cost, power requirements, size of wireless hardware, transfer rates, and ease of implementation came into play in selecting the communication equipment.

The MicroHopper data radio operates in the unlicensed frequency range, has an excellent transmission range, is not susceptible to interference, was readily available, was relatively cost effective, was able to be battery powered, was adequately small, provided proper transmission rates, and was easy to implement. The system was selected so that the BCMs would not recognize that the hard-wire connection had been modified to a wireless connection. By doing this, the system functions with the current software.

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The system is composed of the MicroHoppers, the wiring necessary to connect the BCMs and the laptop to the transceivers, and housings for the transceivers.

The system has been tested to make sure that it performs to the requirements of Square D. The requirements were that the system must demonstrate the wireless interrogator method with at least two BCMs.

Operating Environment

A typical environment where this system might be utilized is an industrial setting. A factory is a good example. Extreme conditions like heat and humidity should not be a factor. However, because this system is wireless, interference from other wireless communication devices using similar bandwidths could be a factor. In addition, electromagnetic interference from the power system associated with the breaker could affect the performance of the system.

Intended User(s) and Use(s)

The initial user for the wireless interrogator system will be Square D Company. Eventually Square D would sell the wireless system as an added feature to their breakers. In this case the user could then be a factory supervisor or maintenance person. If part of the electrical system is having problems, this interrogation method could be a good way for a supervisor or maintenance person to monitor the problem. In addition, the breaker manufacturer or an electrical contractor may want to monitor the equipment they are installing or have installed. The intended use of the wireless interrogator is to provide a reliable way for someone to rapidly interrogate many breakers within a facility. Under the assumption that this system will be used with a laptop computer, the system will provide an efficient way to move around and take breaker readings within a building.

Assumptions

Spread spectrum signal is immune to interference in an industrial environment The 24-volt direct current power supply for the BCMs is sufficient to power the

wireless communications hardware. If interrogation of two BCMs is possible then interrogation of more BCMs will be

successful

Limitations

Interrogation of only 32 BCMs possible due to their memory restrictions Transceiver at laptop end must be powered from serial connection or by battery Devices must attach conveniently to circuit breaker or laptop Operates at a maximum of 19.2 kbps

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Design Requirements

Design Objectives

A wireless communications device to attach to each BCM. The device will make use of the RS-485 serial protocol that is used by the BCMs. It will transfer and receive data using frequency hopping spread spectrum (FH/SS). This device is a wireless transceiver integrated circuit that includes all of the components necessary for spread spectrum wireless communication.

A wireless communications device to attach to the laptop. This device is similar to the device attached to the BCMs. It communicates with the laptop through the RS-232 serial port.

Functional Requirements

The wireless communication devices allow for wireless transmission of data from the BCMs to the laptop.

The wireless system works with the current software

Design Constraints

The wireless link must communicate at a distance of at least 30 feet. Communication at this distance is necessary for an operator to stand near the breakers and retrieve the information in an easy manner.

The information must be transferred at a rate of at least 19.2 kbps. The amount of data being transmitted is very small. A transfer rate of 19.2 kbps is more than an acceptable for this application.

The wireless communications are subject to interference from other communication devices and the circuit breakers themselves. Due to its design FH/SS will avoid interference from other communication devices and the circuit breakers.

The wireless hardware for the laptop must be non-cumbersome and easily mobile. The weight should be below 3 pounds and the size should be below 3 x 3 x 5 inches. A lightweight solution for the power source of the hardware may be obtaining power through the serial port, from the computer, or from a lightweight battery.

The transceivers attached to the BCMs must be able to fit in the circuit breaker housing.

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Measurable Milestones

Wireless communication operates at a 90% success rate. With the existing software having a 90% success rate results in having a valid response from 90% of the polls.

Functional wireless communication distance. The communication should work at a distance of at least 30 feet. This was measured by stepping off rough estimates of various distances and testing the equipment.

The time that is required to transfer information. The system must operate at 19.2 kbps. The software displays the transfer rate. The poll response delay time must be under .5 sec. This is determined by the software, if the response is too slow the response is ignored.

The size of the hardware attached to the laptop. The device must be less than 3x3x5 inches.

Number of breakers that the software can communicate with. The software must be able to communicate with at least 2 BCMs.

End-Product DescriptionThe WCBI consists of a laptop connected to a MicroHopper via an RS-232 serial link and the ModScan 32 interrogator software. A standard 9V battery powers the MicroHopper. The necessary components attached to a circuit breaker to add wireless capabilities are the trip unit, the BCM, and a MicroHopper connected to the BCM with an RS-485 serial connection link. This MicroHopper is powered by the 24 V DC power supply attached to the BCMs. The complete system improves the efficiency of obtaining settings such as level, delay, and the history of tripping events from multiple breaker units. It allows for interrogation of up to 32 different breaker units from a distance of up to approximately 350 feet.

Approach and Design

Technical Approaches

Once a solution was agreed upon, purchasing and designing of the hardware followed. Due to the difficulty of the design and the delay in the arrival of parts, it was decided to pursue a different solution. The final solution consisted of purchasing and implementing the MicroHopper with the current system. Square D emphasized that improvement of the current software was not necessary.

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Technical Design

Figure 1 - Existing system

First Solution:

The first portion of the project involved choosing the appropriate wireless communication devices for the system. Initially the guidelines were that all of the BCMs would still be daisy chained as shown in Figure 1. Only one wireless device would be necessary at the circuit breaker end. This allowed for the removing the RS 232 serial connection and connecting the daisy chain directly to a wireless access point. This led to the development of the following plan.

Figure 2 - First proposed solution

This plan would have been easy to implement and offered the option of using a PDA instead of the laptop. Most of the group effort would have been involved with the creation of new software to work with the system.

After more research the Square D decided that they wanted to break the daisy chain completely and have a separate wireless device for each BCM. The above solution would have worked with the new requirements, but it would have been too expensive and quite impractical to have a wireless access point for each breaker.

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More research was performed and the group decided to develop their own wireless transceiver using transceiver ICs and additional components. Figure 3 shows the 2nd

proposed system.

Second Solution:

Figure 3 – Second proposed solution

The second proposed wireless system would have been created with the addition of ICs that transmit and receive data at the circuit breaker side and the laptop side. The following is a description of the system.

The ICs perform FSK modulation of the serial data and transmit in the 900 MHz range. Also, signal conversion is necessary to insure that the proper voltage levels are achieved and that the signals are compatible with RS 232 for the laptop.

The signal conversion requires RS 485 transmitter and receivers on the breaker (left) side. The RS485 transmitter/receivers convert the differential voltages used by RS485 serial communication to the logic levels necessary for the wireless transmitter/receiver ICs. Signal conversion on the right hand side also requires an RS 485 to RS 232 converter.

Each BCM has a wireless receiver and transmitter IC denoted by RX/TX. The communication takes place in the ISM band of 902-928 MHz. All transmitters and receivers will operate at a frequency of 915 MHz. The 900 MHz ISM band was chosen because it requires no licensing, many cheap ICs are available, and it meets the basic transmission requirements. The 2.4 GHz ISM band was also a valid solution but the ICs are more expensive and complex.

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The ICs use FSK modulation. FSK was chosen because it is very simple, works well with serial data transmission, many circuits include this technique, and it is less susceptible to interference than ASK and OOK.

The receivers/transmitters can operate on the same band because the software uses half duplex master-slave communication. For example RX1 will be receiving the transmissions from TX2 the software will not be reading the input port at this time.

Initially there was concern with switching the receivers and transmitters for communication at the appropriate time. Therefore an alternate solution using multiple channels was developed.

For this plan the BCMs RX and TX operate at different frequencies. The communication takes place in the ISM band of 902-928 MHz. For example TX1/RX1 will operate at a frequency of 910 MHz and TX2/RX2 will operate at 920 MHz. This plan requires the use of good band pass saw filters to filter out the other channel. Also the reference crystals on the evaluation boards will need to be changed.

Final Solution:

After delays and realization of the complexity of creating a new system it was decided to use the MicroHopper transceivers. The system is shown below in Figure 4.

Figure 4 - Final Solution

Initially two transceivers were purchased together in an evaluation kit. This kit included a transceiver with an RS 232 adapter to be used with the laptop, a transceiver with an RS 485 adapter to be used on the circuit breaker side, an RS 232 cord, a power supply, user’s guide, and the software necessary to change settings on the MicroHopper transceivers.

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The transceivers integrated perfectly into the system after a few alterations. It is necessary that the transceivers are set to operate at 19.2 kbps. This is most likely because 19.2 kbps is the serial rate set on the BCMs. Furthermore, the RS 485 adapters are meant to function with two-wire RS 485 and not the four-wire system used by the BCMs. This problem can be alleviated easily by connecting the RX+, TX+, and RX-, TX- lines at the MicroHopper end. Or, these ports may be connected at the BCM end and only two wires are necessary to run to the MicroHoppers. As shown in Figure 5 Transmit A corresponds to TX+ and RX+. Also, Transmit B corresponds to TX- and RX-.

Figure 5 - MicroHopper connector schematic

Table 1 shows the proper wiring for the connectors. Importantly, Red and Green are connected and Black and White are connected.

Wire Color Red Black Green White White RedConnection TX+ TX- RX+ RX- Ground +24V

Table 1 - Wire/Connection relationship

Also, none of the RS 485 transceivers were programmed properly on reception. The RS 485 to RS 232 adapter is not capable of connecting the devices to the computer for programming. Therefore it is necessary to unscrew and swap the RS 485 adapter with the RS 232 adapter. The setting that needs to be changed is the serial protocol. It should be changed from RS 232 to RS 485. Then the RS 485 adapter can be reattached.

Testing Description

Initially the product was tested on equipment provided by Square D. This testing included assuring that the system was stable and performed to the desired requirements. The most basic requirement set by Square D is that interrogation of at least two BCMs at a distance of 30 feet is possible. Initially, the system was tested with one BCM. After communication with one BCM was successful, another MicroHopper was purchased. Communication with two BCMs was then tested and proved to be a success. The product was also tested to demonstrate its ease of use for the end consumer. Square D could

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possibly test the final product in an actual working environment. The product will need met the basic requirements in all of these tests.

Test Results: Interrogation of two BCMs is possible Interrogation works at a distance up to 350 ft. Communication works at 19.2 kbps and a poll response delay of 250 ms Communication success rate of 50% at 350 ft. and 100% within 50 ft.

Risks and Risk Management

The first type of risk encountered was not knowing the project definition clearly and possible solution routes. The risk was managed by choosing a group member to stay in close contact with the client. Furthermore, weekly meetings with the project advisors help to guide the researching of possible solutions. Another risk that was not anticipated was Square D changing the project goals after further reflection and reviewing the original proposal (They decided to remove the daisy chaining of BCMs completely). The impact of this was minimized by working hard to create a new proposal in a timely manner.

Another potential risk was that the new (second) solution would not be successful. In addition, delay in receiving parts for the solution was a concern. Another solution (final solution) was adopted and implemented successfully.

Finally, there was always the risk that a team member would have been lost. Having frequent meetings ensured each group member understood the project solution. Furthermore, the entire group was here to complete the project.

Recommendations for Follow-On Work

Possible future work should include an enhanced prototype version of the product. This enhanced prototype would include more user-friendly software, a USB interface, and lower battery power consumption.

Financial BudgetEquipment and part costs are given in the following table. The actual expenses to date are low due to the fact that the team has received parts for free and/or Square D has purchased them. The expenses for the group consisted of the following items containers, bolts, nuts, power adapters, batteries, and other miscellaneous equipment. The expenses for Square D are as follows:

• $600 transceiver evaluation kit [2 transceivers (RS-232 and RS-485), cables, power supply, software, manuals]

• $100 transceiver (3rd transceiver with RS-485 adapter for testing)

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• $40 shipping for above parts

ItemOriginal Budget

Estimate

Revised Budget

Estimate

Actual Expenses To Date (Group)

Actual Expenses To Date (Square D)

Equipment and Parts $400.00 $800.00 $39.00 $700.00Telephone and Postage $5.00 $5.00 $0.00 $40.00

Printing $50.00 $50.00 $40.00 $0.00Totals $455.00 $855.00 $79.00 $740.00

Table 2 - Financial budget

Personnel Effort BudgetThe following charts contain information on the groups expected time to be spent and the time already spent on the project.

PersonnelOriginal Effort

EstimateRevised Effort

EstimateActual Effort To

DateGreg Stamp 56 hrs. 110 hrs. 122 hrs.Matt Hensler 57 hrs. 80 hrs. 97 hrs.

Fahad Azeem 52 hrs. 75 hrs. 85 hrs.Neil Peterson 55 hrs. 90 hrs. 99 hrs.

Totals 220 hrs. 355 hrs. 403 hrs.

Table 3 - Overall personnel effort budget

Project ScheduleThe Gantt charts below show the original and revised schedule for first semester (August 2001-December 2001) and the original and revised schedule for second semester (January 2002-May 2002). Tasks specific to the project and tasks specific to the course are shown. The revised schedule was due to lack of information and delay in communication between the team and Square D. Also, the constantly changing scope of the project has caused several changes in the original schedule. Finally, major delays in ordering and receiving parts pushed pack the timeline for many of the tasks to be completed in the second semester.

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Figure 6 - First semester schedule (original and revised)

Figure 7 - Second semester schedule (original and revised)

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Evaluation of Project SuccessThe project milestones were fully met. With the initial design plan of first semester the project would have been accomplished early in the second semester. Having a complete change in the design late last semester delayed the project significantly. Some less critical tasks that could not be carried out included an on-site test at Square D, improved software design, and development of better housing for the MicroHoppers. This was also due to the changing scope of the project in the first semester and the unanticipated difficulty in receiving and implementing parts for the alternative (second) solution.

CommercializationThe main purpose of the project was for Square D to develop a working wireless interrogation prototype to demonstrate the feasibility of wireless interrogation of circuit breakers to their marketing department. As result of this, cost was not considered a major factor in the development of this project. However in order to make WCBI a commercial product Square D will be developing their own wireless devices for better fit into their circuit breakers and to reduced cost.

The hardware purchased for demonstration of the wireless interrogation consisted of evaluation board transceivers. These devices result in a more costly system than if Square D manufactured the transceivers themselves.

As a rough estimate, by purchasing the transceiver devices from World Wireless Communications in bulk, the MicroHoppers will cost $100. There will be an additional cost for an antenna and any type of adaptation this device might need to fit into the system. Therefore, the cost to Square D would be around $150 per transceiver. The customers would then have to spend around $200 for each BCM transceiver and each laptop transceiver. An additional cost will be incurred on the customer for software and additional cables.

If Square D manufactures the devices themselves, there will be a significant decrease in cost per device. This cost to the consumer could get as low as $50. This cost is negligible compared to the cost of the circuit breakers themselves.

Square D and its clients would benefit from the use of this device. The market would consist mostly of companies with multiple breaker units. Most of all, companies that have a reliance on power or that are in areas of known power problems would especially benefit from this product.

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Recommendations for Additional Work More user-friendly software would be beneficial. The current software requires

the user to look up what register contains the specific information they need to obtain i.e. time of trip event and then typing in the register address. This system could be replaced by having the information programmed into the software. The use of Visual Basic is a recommended approach to designing the new software.

Adjusting the transmit power on transceiver at the laptop end to increase the battery lifetime.

Development of a transceiver design that can be manufactured in-house.

Lessons LearnedAspects of this project that went well included the poster design, trip to Square D in Cedar Rapids, the presentations, and the increased knowledge of the group members. The best aspect of the project was that it worked properly. There were several things that did not go well with this project. First, the group learned to ensure that the problem definition is well defined. Also, alternative solutions need to be developed in case the project definition is changed. Ordering parts turned out to be problematic. Parts need to be ordered well ahead of deadlines to avoid the problems with shipping delays. Also, contingency plans needed to be put into place if parts are not available in time.

The group gained a great deal of technical knowledge in working on this project. Everyone came away with a better understanding of the serial communication standards (RS-232, RS-485). Also, the group learned about the function of industrial circuit breakers, FSK, wireless communication protocols, and wireless communication devices. Furthermore, the group learned about bandpass SAW filters, crystal oscillators, and antenna design.

In dealing with the client, the group learned a great deal about how things work in industry. The group also learned to specific tasks to each group member to keep on track. Scheduling and meeting deadlines is crucial in successfully completing a project on time. Finally, the group learned that it takes much persistence and direction to make a project successful.

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Project Team Information

Team Members

Name: Neil PetersonMailing address: 232 S. Walnut #16 Ames, IA 50010Telephone number: 515-232-8298E-mail address: npeterso@iastate.eduMajor: EE

Name: Greg StampMailing address: 232 S. Walnut #16 Ames, IA 50010Telephone number: 515-232-8298E-mail address: gstamp@iastate.eduMajor: EE

Name: Matt Hensler Mailing address: 2922 West St #17 Ames, IA 50014Telephone number: 515-268-0374E-mail address: rhens@iastate.edu Major: EE

Name: Fahad Azeem Mailing address: 4231 Hawthorn Court Ames, IA 50010Telephone number: 515-572-7739E-mail address: fahadaz@iastate.eduMajor: Cpr E

Faculty advisors

Name: Glenn HilleslandISU Mailing address: 1111 Coover Ames, IA 50011-3060Telephone number: 515-294-7678Fax number: 515-294-4263E-mail address: hilles@iastate.eduDepartment: ECpE

Name: James TriskaISU Mailing address: 2218 Coover Ames, IA 50011-3060Telephone number: 515-294-4676E-mail address: triska@iastate.eduDepartment: ECpE

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Technical Advisors

Name: Mani MinaISU Mailing address: 2215 Coover Ames, IA 50011-3060Telephone number: 515-294-2663E-mail address: mmina@iastate.eduDepartment: ECpE

Name: Steve RussellISU Mailing address: 2427 Coover Ames, IA 50011-3060Telephone number: 515-294-1273Fax number: 515-294-2663E-mail address: sfr@iastate.eduDepartment: ECpE

Client

Name: Henry ZylstraCompany: SQUARE D CompanyMailing address: 3700 6th Street SW, P. O. Box 3069 Cedar Rapids, IA 52404-5403Telephone number: 319-369-6442Fax number: 319-369-6442E-mail address: zylstrah@squared.com

Name: Gregory S. WieseCompany: SQUARE D CompanyMailing address: 3700 6th Street SW, P. O. Box 3069 Cedar Rapids, IA 52404-5403Telephone number: 319-369-6546Fax: 319-369-6634E-mail address: wieseg@squared.com

SummaryAs noted before, circuit breaker interrogators have become essential in monitoring breaker settings and trip history. However, with the current configuration, users are bound to the breakers by the serial connection. In the current system various problems exist with the wiring between circuit breakers. This project replaces the physical connection to and in between circuit breakers with a wireless link that allows the user to more conveniently interrogate multiple circuit breakers.

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References1. http://www.worldwireless.com/ - World Wireless Communications, Inc2. http://www.maxim-ic.com/ - Maxim ICs3. http://www.melexis.com/home_products.htm -Melexis Product Selection Guide4. http://www.infineon.com/cmc_upload/documents/028/947/TDA5102_V1.1.pdf -

Infineon Technologies5. http://www.rfmd.com/online_catalog_frameset.asp?page=DataBooks/db97/

db97toc.htm&loc=Transceivers - RF Micro Devices, Transceivers6. http://www.silabs.com/products/RFSyn_4133.asp - Silicon Laboratories, Products

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